Electrical musical instrument

ABSTRACT

Each of two related systems produces narrow bands of electrical &#39;&#39;&#39;&#39;noise&#39;&#39;&#39;&#39; corresponding to pipe-organ steady wind-noise components peculiarly related in frequency to the harmonics of a main (steady-state) tone. In the first system, &#39;&#39;&#39;&#39;white&#39;&#39;&#39;&#39; noise from a noise generator is filtered by a plurality of narrow-bandpass filters to obtain the narrow bands of noise. In the second system, the output of a noise generator is passed through a lowpass filter to provide a modulating voltage which is applied to a pair of photocells, whose resistance is photoelectrically varied sinusoidally (180* out of phase) with time, to obtain each narrow band of noise. In both cases, the narrow bands are combined with the main tone and converted to sound in an electro-acoustic output system.

United States Patent 1191 Jones et a1.

[ ELECTRICAL MUSICAL INSTRUMENT [75] Inventors: Edward M. Jones, Cincinnati, Ohio;

William C. Wayne, .lr., South Fort Mitchell, Ky.

[52] US. Cl 84/l.l9, 84/l.l8, 84/122,

84/123 [51] Int. Cl. G10h 11/06, GlOh 5/00 [58] Field of Search ..84/1.01,1.04,1.11,l.18,

84/1.19, 1.22, 1.23, 1.24, DIG. 5

14 1 Feb. 25, 1975 3,711,620 1/1973 Kameoka et a1. 84/124 Primary Examiner-Richard B. Wilkinson Assistant Examiner-Stanley J. Witkowski Attorney, Agent, or Firm-Burmeister, York, Palmatier, Hamby & Jones [57] ABSTRACT Each of two related systems produces narrow bands of electrical noise corresponding to pipe-organ steady wind-noise components peculiarly related in frequency to the harmonics of a main (steady-state) tone. In the first system, white noise from a noise generator is filtered by a plurality of narrow-band-pass filters to obtain the narrow bands of noise. In the second system, the output of a noise generator is passed through a low-pass filter to provide a modulating volt- [56] Rehrences Cited age which is applied to a pair of photocells, whose re- UNITED STATES PATENTS sistance is photoelectrically varied sinusoidally (180 2,694,954 11/1954 Kock s4/1.01 x out of p as t time, to obtain a narrow band 3,476,865 11/1969 Bereskin 84/104 of noise. In both cases, the narrow bands are com- 3,479.440 1 H 69 a t n et a X bined with the main tone and converted to sound in an Wayne electro acoustic output system 3,557,295 1/1971 Adachi 84/l.18 3,598,891 8/1971 Adachi 84/124 12 Claims, 12 Drawing Figures I 1 1 22 B P F 20 \6 t8 1 Wl'HTE NOt'5E B P F 28A 19 l B P F I I SteNm. SouRcE SHEET 10F 5 SIGNAL. SouRcE MIX.

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SHEET 0F 5 PATENIEU FEB25 I975 3.867, 862 SHEET 50F 5 FIGJO look 100K 312 A). NORMAL 27M; .039

270K amvE-RTED 3x4 68041 M .o47mf [00K SOMF (NON-POLARIZED) 320 316 FIG. LL

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LIGHT MODULATION 2P5 v a QomR 6; FREQUENCY) MIRROR g lMAGE 3; #3 322 ZFB 32s FREQUENCY ELECTRICAL MUSICAL INSTRUMENT BACKGROUND OF INVENTION Several prior art patents exist in which random electrical noise is employed in electronic organs to simulate certain wind-noise characteristics of pipe organs. Markowitz US. Pat. No. 3,327,044; Wayne US. Pat. Nos. 3,390,223 and 3,505,462; and Adachi US. Pat. Nos. 3,557,295; 3,598,891 and 3,609,201 are examples. Kock U.S. Pat. No. 2,694,954 keys random electrical noise through a series of sharply tuned, band-pass filters, one for each semi-tone of the scale, to achieve a chorus effect. It remained for the present inventors, in studying the tones of certain organ pipes (such as the Principal), to discover that tones contain a plurality of narrow bands of uncorrelated random noise, which bands have center frequencies occurring at approximately the same frequencies as certain lower harmonics of the tone and between certain higher harmonics of the tone. The bands of noise which occur between higher harmonics of the tone are believed to result from the fact that the normal modes of a pipe are not true harmonics due to an end correction which is a function of frequency.

SUMMARY OF THE INVENTION Prior to transduction to sound of an electrical signal corresponding to an organ tone, narrow bands of uncorrelated, random, electrical-noise signals are combined with the tone signal, the bands of noise signals having center frequencies l substantially equal to the lower harmonics of the electrical tone signal, and (2) about mid-way between certain higher harmonics of the electrical tone signal. Further, the present inventors have found that the bands of electrical noise have center frequencies preferably located on a plurality of semi-tones above the fundamental frequency of each tone, the bands being located on semi-tones selected from the 12th, 19th, 24th, 28th, 29th, 30th, 32nd, 33rd, 34th, 35th, 37th, 39th, 41st, 42nd, 44th, 45th, 46th, and 47th above the fundamental frequency of the tone. Therefore, a musical instrument can be constructed providing only those noise bands which have center frequencies on the semi-tones of the musical instrument, and the inventors have further found that these semitones need only be in the frequency range from about 262 Hz to about 8,372 Hz. The bands of electrical noise signals (for combination with the electrical tone signal) may be produced in a number of ways, and the present patent illustrates two embodiments of the invention. In one embodiment the bands of electrical noise signals are generated by passing a wide spectrum electrical noise signal through a plurality of narrow band-pass filters and electrically combining the output of the filters in proper combinations for each tone. In the second embodiment, the bands of electrical noise are generated by conducting an electrical noise signal generated by a white noise source through one or more low-pass filters and using the resulting signal to modulate a plurality of pairs of photocells, each photocell being light modulated at the frequency of one of the tones of the instrument. Economy of circuitry is achieved by limiting the center frequencies of the narrow bands to appropriate semi-tones of the musical scale.

The principal object of this invention is to provide an electrical musical instrument which more closely simulates the tonal qualities of a wind blown pipe than prior electrical instruments, and in particular simulates the steady wind noise which characterizes certain pipe organ tones.

A more specific object of this invention is to provide an electrical musical instrument with means to add a low-level noise spectrum to the series of regularlyspaced spectral lines representing the harmonics of an electronically, electromagnetically, electrostatically or photoelectrically generated organ tone, that noise spectrum consisting of a plurality of narrow bands of uncorrelated noise having center frequencies located approximately on the lower harmonics of the tones of the instrument and between the higher harmonics of the tones of the instrument.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a subcombination of a musical instrument generally illustrating the present invention;

FIG. 2 is a block diagram of one species of the system of FIG. 1;

FIG. 3 is a block diagram of another species of the system of FIG. 1;

FIG. 4 is a partial-block, partial-schematic diagram of still another species of FIG. 1;

FIG. 5 is a block diagram illustrating the apparatus for producing a single tone for a musical instrument in accordance with another embodiment of the present invention;

FIG. 6 is an expanded partial-block, partialschematic diagram of the musical instrument of FIG. 5;

FIG. 7 is a fragmentary partly-diagrammatic view taken along the line 7-7 of FIG. 6;

FIG. 8 is the detailed circuit diagram of a band-pass filter for use in the musical instrument of FIG. 6;

FIG. 9 is a partial-block, partial-schematic diagram of another species of the invention of FIG. 1;

FIG. 10 is a detailed schematic diagram of a low-pass filter for use in the system of FIG. 9;

FIG. 11 is a schematic diagram of the operational amplifiers of FIG. 10; and

FIG. 12 is a chart showing noise-band curves.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS FIG. 1 illustrates in diagrammatic form the apparatus for producing a single tone of an electronic organ in accordance with the present invention. The illustrated electronic organ has an electrical signal source 12 which may be any one of the many types of sources of electrical tone signals known in the art of electronic organs, such as electronic, electrostatic, photoelectric or electromagnetic. A source 14 of electrical noise bands, selected in accordance with the invention as discussed in detail hereinafter, feeds its output into a suitable mixing circuit 16, the output of which is combined with the signal from source 12, and both are converted into sound in an output system, which comprises an amplifier l8 and an electroacoustic transducer 19. Thus the sound emanating from this transducer 19 has, in accordance with the invention, a noise component or wind noise comparable to the sound'ernanating from certain organ pipes for example, the Principal or the Flute.

FIG. 2 diagrammatically illustrates the first of the two preferred embodiments of the invention for producing a single tone of an electrical organ, namely apparatus in which the source of noise bands utilizes a wide band noise source and a plurality of band-pass filters. In this embodiment, a white noise electrical generator 20 has its output connected through a key switch (or keyswitched gate) 22 to a group of parallel-connected, narrow-band-pass filters, of which ones 24, 26 and 28 are shown as blocks BPF. Suitable level-setting resistors 24a, 26a and 28a may be inserted at the input of each filter, as shown, to proportion noise components in correct amplitude ratios. The outputs from the bandpass filters 24, 26 and 28 are combined at the mixer amplifier 16 for conversion to sound in the output system 18, 19. The output of a tone-signal source 12 is connected to the junction at the output of the mixer 16, and the signal from the tone signal source 12 is controlled by a switch 32 ganged to switch 22.

FIG. 3 bears similarity to FIG. 2 so far as the noise is concerned, and similar elements have the same indicia. However, the signal source of FIG. 3 comprises a tone signal generator 36 keyed-on by switch 32 from a source (not shown) of an appropriate activating potential v.

Although FIGS. 2 and 3 show keying of the output of the noise generator, it is preferred to gate the output of the filters as illustrated in FIG. 4. Also, FIG. 4 illustrates diagrammatically that apparatus for producing more than one tone of a musical instrument.

In FIG. 4, the output of the signal source 12 is shown keyed by switch 32 to a collector 33 (for other tone signals). The collector 33 is shown connected to distributor 35 for tone-color filters, such as the one 37, whose output is passed to the output system by stop switch 39. A collector41 passes outputs of other tone color filters (not shown) to the amplifier 18 and loudspeaker system 19. Concurrently, the white noise source 20, which may have several outputs as shown, feeds band-pass filters 24, 26 and 28, whose outputs are shown leveled by resistors 25, 27 and 29, respectively, for mixing, as shown, at the amplifier 16. Moreover, output of amplifier 16 is shown entering a suitable electronic gate 31 (detail appears later herein). The output of gate 31 and others (not shown) is collected by line 47 for amplification by noise amplifier 49 and leveling by resistor 51. At junction 53, the noise bands are shown meeting tone signal output from tone color filter 37 for combined amplification by amplifier 18 and conversion to sound at transducer 19. The gate 31 is actuated concurrently with tone signal from generator 12 by a direct current voltage from a source of potential V, as keyed by switch 53 ganged to switch 32.

Referring now to FIG. 5, two uncorrelated white noise generators WN =1? l and WNat= 2 are shown to demonstrate how a series 38 of band-pass filters can be connected to the noise generators to achieve as much uncorrelation as possible in a practical embodiment. Before describing the elements of FIG. 5, however, it is desirable to explain in more detail the realization that there is a usable relationship between the semi-tones of the equally tempered scale and their harmonic number referred to a given fundamental frequency. Nonintegral multiples of a fundamental are usually referred to as partials of the fundamental but are here listed also in the harmonic number column. Reference is made to the following chart:

Semi-Tones Harmonic Semi-Tones Harmonic (above Number (above Number fundamental) fundamental) 0 l 35 7.56 12 2 36 8.00 19 3 37 8.48 24 4 38 9.0 25 4.24 39 9.5 26 4.49 40 10.0 27 4.76 4l 10.7 28 5.04 42 l 1.3 29 5.34 43 12.0 30 5.66 44 12.7 31 6 45 13.5 32 6.35 46 14.2 33 6.72 47 15.1 34 7.12

Since an actual C organ pipe (Principal type), upon analysis, has been found to have noise peaks coinciding with lower harmonics, namely the second through the fifth, but interspersed between the higher harmonics, namely the sixth through the tenth, semi-tone-related noise filters may be used per the above chart. FIG. 5 sets forth a specific example for the noise components associated with the C Principal. The filters 38 of FIG. 5 are numbered 38(C 38(G 38(C 38(F 39(B 38(C- =1? and 38(D #l= the designation in the parenthesis identifying the center frequency of the band pass filter in terms of a semi-tone. Hence, the noise components for the C Principal tone are achieved as follows: Band pass filter 38(C provides the noise band corresponding to the second harmonic of note C since C is the 12th semi-tone above the note C band-pass filter 38(G provides the third harmonic since G is the 19th semi-tone above C bandpass filter 38(C provides the fourth harmonic since C is the 24th semi-tone above C band-pass filter 38(F provides the sharp fifth harmonic since F is the 29th semi-tone above C band-pass filter 38(B provides the noise band centered between the seventh and eighth harmonics of tone C since B is'the 35th semitone above C band-pass filter 38(C 41:) provides the noise band centered between the eighth and ninth harmonies since C =11: is the 37th semi-tone above C and band-pass filter 38(D =ll= provides the noise band centered between the ninth and tenth harmonics, since D is the 39th semi-tone above C Since the frequency relationships of the preceding table are true for all semi-tones, proper bands of noise may be combined for other tones, and in proper proportions, using the outputs of some of the same and additional filters in different combinations.

The outputs of the narrow-band filters 38 are to be combined with the C tone generated by the instrument in a conventional manner. In this particular construction, the C tone is activated by closure of switch 40 which applies a potential to a suitable envelope circuit 42, which in turn is connected both to a gate 31 and to a second envelope circuit 46 feeding a tone signal generator 48. The tone signal generator 48 is preferably, but not necessarily of a photoelectric type, as disclosed in US. Pat. No. 3,023,657 to Jones and Love, US. Pat. No. 3,249,678 ofJones, and US. Pat. No. 3,529,070 of Jones, and is activated by the keying signal from the envelope circuit 46. The envelope circuits 42 and 46 are for the purpose of shaping the attack of the keying signal for the gate 31 and signal generator 48, respectively.

The outputs of filters 38(C 38(G 38(C 38(F 38(B 38(C and 38(D are conducted through suitable scaling resistors 50, 52, 54, 56, 58, 60 and 62, respectively, to a mixing amplifier l6 and hence to a gate 31. The noise output of gate 31, is activated by the keying signal from the first envelope circuit 42, and is conducted to a suitable amplifier 66. The output of amplifier 66 is adjusted in amplitude by resistor 67 and combined with the output of the generator 48 at the input of an amplifier 70, which may comprise a preamplifier and power amplifier, for conversion to sound in a loudspeaker system 72.

Referring back to the distribution of the outputs of uncorrelated noise sources WN 1 and WN 2 (FIG. 5), it can be seen that filters 38(C and 38(G are fed by WN 1; filters 38(C 38(F and 38(B are fed by WN 2; and filters 38(C and 38(D are also fed then by WN #1. This distribution is based on the premise that correlation of noise will be minimized when adjacent octaves of semi-tones are fed from different noise sources. Obviously, still greater lack of correlation of noise can be achieved by using a separate white noise source for the semi-tones of each octave.

The inventors have found that in an instrument of full range, 61 filters are sufficient, that is one for each of the semi-tones from values for filters covering the range from C (262 Hz) to C (8,372 Hz). It should be noted here that C, was chosen as the lower limit for noise bands, because the human ear does not respond very well to low-level noise signals below 262 Hz. It will be noted that Q-values (sharpness of resonance) for noise bands are shown in FIG. 5 as progressing from Q l4 for filter 38(C to Q= for filter 38(D The Q values determine the width of the noise bands, and the inventors have found that for the 61 semi-tones between C, and C the Q values should increase with frequency from Q=l3 to Q=24.

FIG. 6 illustrates two consecutive semi-tones and two consecutive footages of the musical instrument set forth in FIG. 5 in the form ofa photoelectric organ, and like reference numerals followed by identifying letters have been used to identify corresponding elements. Key switches 40(C and 40(C represent notes C and C respectively, and are connected between a source of DC. actuating potential V and envelope networks 42(C and 42(C respectively. Networks 42(C and 42(C not only supply the desired actuating voltage envelope to the gates 31A, 31B, 31C, and 31D, connected as shown via emitter-followers 90 and 92, respectively, but also perform a key-click suppression function by virtue of the high-frequency, by-passing effect of capacitors 94(C and 94(C respectively. Also, envelope networks 42(C and 42 (C feed secondary envelope circuits 46 (C and 46 (C respectively. Upon closure of keys with 40 (C the C envelope network 46 (C supplies an increasing transient D.C. voltage to photocells 102 and 104, operating in push-pull (as indicated by arrows pointing in different directions) according to the teachings of the mentioned patents of Jones and Love.

Modulated light from a source diagrammatically shown as a lamp 74 falls upon the pairs of photocells 102 and 104, 106 and 108, 110 and 112, and 114 and 116. The light is modulated by means of a rotatable pitch disc 76 driven by a motor 78 which is disposed between the lamp 74 and a stationary voice disc 80. The disc 76 has a transparent member 82, which may be constructed of glass, and an opaque film 84 on the surface thereof confronting the stationary voice disc 80. A plurality of tracks 86 (FIGS. 6 and 7) disposed concentrically about the center of the disc 76 contain alternating transparent slots 87a separated by opaque areas 87b, (FIG. 7). The tracks 86 of the pitch disc 76 are aligned with transparent tracks 88 in an otherwise opaque film 89 disposed on a transparent member 91 of the voicing disc 80. The tracks 88 contain wave form patterns, which may be variable area or variable density, and which, in conjunction with the rotating slots 87a of the pitch disc 76, provide modulated beams of light falling upon the photocells. It will be noted that as illustrated the modulation rate of the light falling upon the pair of photocells designated 102 and 104 must produce the C note frequency, the frequency of the modulated light falling upon the pair of photocells 106 and 108 must produce the C note frequency, the modulating light falling upon the pairof photocells 110 and 112 must produce the C frequencies and the modulated light falling upon the pair of photocells 114 and 116 must produce the C frequencies.

FIG. 7, in simplified form for purposes of clarity, illustrates the relationship of the pitch disc 76, voice disc 80, and photocells. The pairs of photocells 102 and 104; and 110 and 112 are illustrated in an assembly 91A which has an electrically insulating base 93, a strip of photoresistive material 95, and electrodes 97 disposed parallel to each other and to the direction of rotation of the pitch disc 76 on the photoresistive strip 95.

It will be noted that each of the photocells 102 and 104 confront a different track 88a and 88b on the voice disc 80, but that both of said tracks 88a and 88b of the voice disc 80 confront the same track 86 of the pitch disc. By locating transparent areas of the track 88a adjacent to opaque areas of the track 88b, the photocells 102 and 104 will produce out-of-phase electrical signals which will add across the autotransformer 118, but the direct current component and transients will cancel, as more full explained in U.S. Pat. No. 3,023,657 of Jones and Love.

Envelope network 46 (C (FIG. 6) also supplies an activating voltage, which has a faster rise time, to photocells 106 and 108, modulated similarly to photocells 102 and 104, except that the scanning slots are twice in number per revolution and the waveform patterns in the voice disc are of different character from the patterns for cells 102 and 104. Thus, the cells 106 and 108 may be used to produce a 4 foot Flute, for example, while cells 102 and 104 may be used to produce an 8 foot Principal.

In a similar manner, envelope network 46 (C activates photocells 110, 112 for the 8 foot voice at note C while photocells 114, 116 are used to produce the 4 foot voice at note C A center-tapped auto transformer 118 collects the signals from photocells 102, 104, 110, 112, and cancels the DC. transients applied to the photocells. Leads 120, 122 carry the tone signals to a preamplifier 124, followed by stop switch 126 and power amplifier 128 to loudspeaker system 130 for conversion to sound. Similarly, the signals from cells 106, 108, 114, 116 employ an auto transformer 132 for pre-amplification by preamp 134 and are made available in the loudspeaker system 136 via stop switch 138 and power amplifier 140.

Having described the manner in which the C and C tones are generated, consideration of the wind sound generating system of the instrument of FIGS. 5 and 6 follows. The notes C and C have been chosen for illustration, because they are below the C level mentioned above as the lower limit for noise bands. Thus, the lowest band of noise for note C is a filtered E (the lowest appropriate noise band above C which corresponds to approximately the fifth harmonic of C (E is 28 semi-tones above C as may be checked on the chart shown above. Therefore, bandpass filter 38 (E fed from noise generator WN 2 feeds a noise band centered at E and leveled by resistor 153 through mixer amplifier 16 (C to gate 318. Gate 31B is closed by actuation of key 40 (C thus permitting the C noise to drive noise amplifier 148. The noise-band output of amplifier 148 has its level set by resistor 150 before being combined at point 152 with the tone signals processed by auto transformer 118.

In addition to a noise band with a center frequency at E the noise components for the C note require noise bands with center frequencies corresponding to the semi-tones G B C D F and G (the latter three not being shown). A narrow band filter 38 (G is connected between white noise generator WN 2 and amplifier 16 (C through a leveling resistor 154 to add the G component of the noise. In like manner, a narrow band filter 38 (B is connected between the white noise generator WN# 2 and the amplifier 16 (C through a leveling resistor 156 to add the 8., noise component. The C noise component is derived from the white noise generator WN 1 in order to increase the uncorrelated nature of the noise and a narrow band filter 38 (C is connected between this generator WN l and the amplifier 16 (C through a leveling resistor 158.

The output of the C noise amplifier is conducted to the 8 foot noise amplifier 148 through gate 318. The output of amplifier 148 is leveled by resistor 150 and combined at 152 with the C tone signal. The C tone signal and C noise signal are amplified by pro-amplifier 124 and conducted to a power amplifier 128 through stop switch 126 for conversion to sound by the speaker system 130. The C noise bands are produced in a similar manner in the embodiment of FIG. 6, that is, by use of a plurality of narrow band filters connected between the white noise generators WN 1 and WM 2 and a mixer amplifier 16 (C through leveling resistors. Only one of the narrow band filters 38(F for the F semi-tone has been illustrated to simplify the drawings, and it is shown connected to the mixer amplifier 16 (C through leveling resistor 160. Other leveling resistors 162 are illustrated connected to the input of the mixer amplifier 16 (C to show the manner in which the noise bands also are combined to form the C noise signal.

The output of the mixer amplifier 16 (CC is connected through a gate 31D for connection to point 164 and to the input of the 8 foot noise amplifier 148. Hence, when the C key switch 40(C is closed, gate 31D is closed, and the C noise signal is included in the 8 foot noise signal of the instrument.

If a 4 foot voice (with steady noise) is desired, stop switch 138 is closed, and one or more of the key switches are closed. key switch 40(0 and 40(C for notes C and C having been illustrated in FIG.

6. Taking C for example, envelope circuit 46(C is activated through envelope circuit 42(C and the pair of cells 106, 108 are fed actuating direct current through conductor 166, thus producing a C signal (an octave above C for the 4 foot voice in response to the light modulation of the pair of photocells 106 and 108. The 4 foot voice is produced in the speaker system 136 through autotransformer 132, preamplifier 134, stop switch 138 and power amplifier 140.

The steady noise bands for the 4 foot C voice are produced by means of a system using the white noise generator WN 1, a plurality of band pass filters connected to the white noise generator WN 1, of which only band pass filter 38(C is illustrated, a mixer amplifier 16(C gate 31A (as actuated by the key switch 40(C through the envelope circuit 42(C and emitter follower and line 174), 4 foot noise amplifier 176, line 178 and level-setting resistor 180. Note that the first band pass filter 38(C for this tone is tuned to the fourth harmonic of the C tone signal instead of the fifth harmonic. Furthermore, for higher pitches even lower harmonics are used. For tones E and higher. the noise bands are tuned to the fundamental and only a few harmonics. It will be noted that the combination of the noise for the 4 foot voice and the C tone signal itself occurs at point 182.

In like manner, the noise bands for the 4 foot C tone are generated by means of the white noise generator WN 1. a group of narrow band filters of which only filter 38 (C for the C noise component is shown, mixer amplifier 16 (C gate 31C and 4 foot noise amplifier 176. It will thus be noted that the narrow band filter 38 (C is utilized in producing a part of the C noise signal as well as a part of the C noise signal. The requirements for the steady noise provision for 6l-note keyboards and two footages are 61 narrow band filters 38 producing noise bands from C to C 73 mixer amplifiers 16, 122 gates. 31 per keyboard, and separate noise amplifier 148 and 176 for each footage of each keyboard. If a third footage is desired (such as 16 foot or 2 foot), 12 additional mixer amplifier 16, 61

additional gates 31 per keyboard and one additional noise amplifier per keyboard will be required.

Referring to FIG. 8, a suitable circuit for the filters 38 with componentvalues for the C band-pass filter 38 (C are shown. Input from a noise generator is applied at point 188 and passes through resistor 190 to point 192, from which there is: (a) a resistor 194 to ground, (b) a resistor 106 and capacitor 198 to output point 200, and (c) a path via capacitor 202, point 204 and operational amplifier 206 to point 200. Also, a resistor 208 is shown in parallel with operational amplifier 206, which is preferably a Motorola No. 748, well known in the electronics art as an integrated circuit having extremely high gain. The filter is very similar to that shown in FIG. 3 on page 76 of Active Inductorless F ilters, edited by S.K. Mitra and published in the U.S.A. by IEEE Press (copyright 1971 Library of Congress Card 70-179914), and the characteristics and operation of such filters are there described.

FIG. 9 illustrates another embodiment of this invention for producing narrow bands of steady noise having fixed center frequencies. It, too, is shown as being applied to a photoelectric organ, although it will be obvious to one skilled in the art that the teachings herein are not limited thereto. Since, in a photoelectric organ, photocells are available whose resistance can be varied sinusoidally at the various semi-tone frequencies, low frequency random noise is used to activate a given photocell (pair) receiving sinusoidal light variations. By using doubly-balanced modulation, neither the lowfrequency noise itself nor the sinusoidal tone is present in the photocell output, but just the two side bands of noise, giving a total bandwidth of twice that of the low frequency noise. (This will be discussed later with reference to FIG. 12.)

FIG. 9 shows a complete system for one tone signal and one band of noise, with ancillary elements and connections which are believed sufficient to illustrate the system adequately to one skilled in the art without adding unnecessary complexity to the figure. Describing first the tone-signal portion of the system, a source of activating potential V is applied at the point 210, and the point 210 is connected to all of the key switches of the instrument, the key switch 212 for C being illustrated. Key switch 212 is connected to an envelope circuit 214, which has'an output point 216. To point 216 is connected an emitter follower EF# 1, having an output point 218, from which activating potential may be obtained for a fast-onset photocell (not shown). Following point 218 is a second envelope circuit 220, to the output of which is connected another emitterfollower EF 2, with an output point 222, from which activating potential may be derived for a medium-onset photocell (not shown). Still another envelope circuit 224 follows point 222 and emitter follower EF# 3 for supplying activating potential to slow-onset photocells 226 and 228. The tone signal developed in the cells 226 and 228 passes through auto transformer 230 (for DC. transient cancellation) and proceeds through preamplifier 232, stop switch 234 and power amplifier 236 to speaker system 238 for conversion to sound.

Still referring to FIG. 9 for the description and operation of the noise-band portion of the system, noise generators 240, 242, 244 are three, of preferably five, white noise sources. Each noise generator is connected to the input of preferably five low-pass filters of which only one is illustrated, namely low pass filters 246, 248 and 250, respectively, Each of the low-pass filters 246, 248, 250 are of a type which is illustrated in FIG. 10 to be described. Choosing generator 242 and low-pass filter 248 for purposes of illustration, the latter is shown connected to three parallel pairs of photocells 252 and 254; 256 and 258; and 260 and 262, representing noise-band notes D E and F The junction 264 between the pair of photocells 260 and 262 is connected to an emitter follower 266, followed by a leveling resistor 268, which is one of a group 270 of seven resistors corresponding to notes F,, A C D E F G and which are, respectively, 28, 32, 35, 37, 39, 41, 43 and semi-tones above the note C keyed to switch 212. The collecting line 272 is connected to each of the resistors 270 and to an input terminal 273 of a mixer amplifier 276. The mixer amplifier has a biasing resistor 278 (between a junction 274 and a negative d.c. supply point 279), a second biasing resistor 280, connected between junction 274 and the base of a transistor 282. A leveling resistor 281 connects the base of transistor 282 with a positive d.c. supply point 283. The emitter of transistor 282 is grounded, and the collector is returned to junction 274. The output from amplifier 276 is connected to the input of gate 284, which is operated by emitter-follower EF which is connected at point 216 to envelope circuit 214.

In the illustrated instrument, there are 6] gates for each footage or stop provided, and each gate has a resistor 286, a resistor 288 and a diode 290 interconnected in a common junction as shown in FIG. 9. The output of the gate (from the diode 290) is connected to line 293 (common to the output of the other gates) and line 293 is connected to the input of a noise amplifier 294. The noise amplifier 294 has a diode 296, a bypass capacitor 298, transistor 300 and biasing resistors 302 and 304, the latter being fed negative direct current from a supply point 305. A leveling resistor 310 is connected between the output terminal 306 of amplifier 294 and point 308 at the input of the preamplifier 232.

Still referring to FIG. 9, the noise generator 240 is followed by low-pass filter 246, feeding another group of three adjacent pairs of photocells designated C,, C, and D The junction point between each pair is connected to an emitter-follower (not shown) which corresponds to the emitter follower 266 for the F, noise component, and the output of each of these emitter followers is connected to a mixer amplifier similar to 276 or one or more of the corresponding mixer amplifiers (not shown).

Regarding the operation of the system of FIG. 9, the wide-band noise signal from generator 242 is processed devoid of direct current (as will be discussed later with reference to FIG. 10) by low-pass filter 248 into 21 normal" output and an inverted output for feeding lowfrequency noise voltages into the photocell pairs 252 and 254; 256 and 258; and 260 and 262, shown as variable resistors.

Push-pull light modulation, as illustrated in FIG. 6 and of the same type described in US Pat. No. 3,023,657 of Jones and Love. is applied to the photocells 252 and 254. Photoresistors 252 and 254 are, on the average, equal, but as 252 goes up in resistance due to light decrease, resistor 254 goes down in resistance due to light increase and vice versa. For a short given instant of time, the normal noise voltage is positive, while the inverted noise voltage is equally negative. During that instant, there are several cycles of light variation at an audio-frequency rate, (D 4? frequency in the case of photocells 252 and 254) the output at the junction 253 being positive after the light is maximum on resistor 252 and is minimum on 254, and the output being negative half an audio cycle later, when the light is minimum on resistor 252 and maximum on resistor 254. This output voltage at junction 253 is therefore an alternating current audio signal which is modulated in amplitude by the noise voltage. Since at a later instant, the normal noise voltage might become negative and the inverted noise voltage positive as a result of random change, the phase of the audio output would be reversed at that time. The phase shifts l at the zero crossings of the noise, but this is still essentially amplitude modulation, and the two side-bands are correlated in a way that is different from frequency modulation.

A truly random band of noise would be equivalent to a combination of amplitude and frequency modulation of the center frequency; but, with the low levels and high modulation rates involved, the ear does not notice that the pure amplitude modulation of a carrier by low frequency noise is any different from a band of noise centered at the same frequency as the carrier. The ear would notice, however, if all the bands of noise making up the noise spectrum of a tone were produced by correlated amplitude modulation of the carriers. It has been found that three adjacent semi-tones may be processed by the same modulation without introducing too much correlation. This means that 61 noise bands can be generated even though the number of low-pass filter-inverters is reduced by 20. Onlyfive noise generators are required. By using them in rotation," the groups of frequencies using the same noise source can be separated by semi-tones, which means that the band widths differ by about 2:1, which minimizes the correlation between these groups.

FIG. 10 illustrates the low-pass filters used in the embodiment of FIG. 9 and gives the values of the low-pass filter 248 for driving the photocells 252 and 254 for the D noise band. The low-pass filter 248 uses two operational amplifiers 312 and 314, and the details of prototype operational amplifiers 312 and 314 (which may, if desired, be integrated circuits) are illustrated in FIG. 11, in which the terminals, labeled and correspond to the and leads of the amplifiers 312 and 314. In an exemplary circuit only three conventional transistors 316, 318 and 320 of FIG. 11 are needed to amplify small differences of voltage between the and input terminals.

Referring to FIG. 12, curve 322 shows the response of a low-pass filter of the type illustrated in FIG. 10. When the sinusoidal light modulation (previously referred to) at audio angular frequency W is applied to a pair of photocells, such as ones 252 and 254 (FIG. 9), the indicated envelope containing the low-frequency noise modulation voltages output from a low-pass filter (as shown in FIG. 10) per curve 322 become as shown in curves 324 and 326. These curves are, respectively, a replica and mirror image of envelope curve 322 and represent the tuned noise which exists at point 253; The dashed-line curve 328 is a typical response curve of a band-pass filter of the type illustrated inFIG. 8.

The invention claimed is:

1. An electrical musical instrument having a plurality of musical tones corresponding in frequency to the semi-tones of the equally tempered musical scale including an electrical tone signal source for each of the musical half-tones of said instrument, elect-ro-acoustic output means electrically coupled to said sources of tone signals, a plurality of electrical switches, a different one of said switches being electricallycoupled to each electrical tone signal source for selectively controlling excitation of the electroacoustic output means, and a source of electrical noise characterized by the improved construction wherein the source of electrical noise has means for generating a plurality of bands of electrical noise, said bands having center frequencies differing approximately by by half-tone steps from each other, and electrical circuit means responsive to each of the electrical switches for coupling a plurality of bands of electricalnoise to the electro-acoustic output means, each of said plurality of bands having bands with center frequencies approximately equal to harmonics of that electrical tone signal source coupled to the same electrical switch.

2. An electrical musical instrument having a plurality of musical tones corresponding in frequency to the semi-tones of the equally tempered musical scale including an electricaltone signal source for each of the musical half-tones of said instrument, electro-acoustic output means electrically coupled to said sources of tone signals, a plurality of electrical switches, a different one of said switches being electrically coupled to each electrical tone signal source for selectively controlling excitation of the electro-acoustic output means, and a source of electrical noise characterized by the improved construction wherein the source of electrical noise has means for generating a plurality of bands of electrical noise, said bands having center frequencies differing approximately by half-tone steps from each other, and electrical circuit means responsive to each of the electrical switches for coupling a plurality of bands of electrical noise to the electroacoustic output means, each of said plurality of bands having a band with a center frequency approximately equal to a harmonic of a group one through five of that tone signal source coupled to the same electrical switch and a band having a center frequency between adjacent harmonics greater than the fourth harmonic of said tone signal source.

3. In an electronic organ of the type having in tandem a tone signal generator, a key switch, a tone-color filter, a stop switch and an electroacoustic output system, the combination comprising a source of narrow bands of electrical noise, said bands having center frequencies respectively corresponding to at least a plurality of the semi-tones above the tone signal derived from said tone signal generator by closure of said key switch of the group consisting of the 12th, 19th, 24th, 28th, 29th, 30th, 32nd, 33rd, 34th, 35th, 37th, 39th, 41st, 42nd, 44th, 45th, 46th and 47th partial, and circuit means coupling said source to a point between said key switch and said stop switch for combining said bands with said tone signal.

4. The combination according to claim 3, wherein said source of narrow bands comprises a widespectrum electrical noise generator, a plurality of narrow-band-pass filters coupled in parallel to said noise generator, second circuit means coupled to said narrow-band-pass filters for mixing said bands, and an electronic gate between said second circuit means and said point between said key switch and said stop switch.

5. The combination according to claim 4, wherein a plurality of leveling resistors are located between respective ones of said narrow-band-pass filters and said second circuit means, and wherein a noise amplifier and a further leveling resistor lie in series between said gate and said point between said key switch and said stop switch.

6. An electrical musical instrument having a plurality of musical tones corresponding in frequency to the semi-tones of the equally tempered musical scale including an electrical tone signal source for each of the musical half-tones of said instrument, electro-acoustic output means electrically coupled to said sources of tone signals, a plurality of electrical switches, a different one of said switches being electrically coupled to each electrical tone signal source for selectively controlling excitation of the electroacoustic output means, and a source of electrical noise characterized by the improved construction wherein the source of electrical noise has means for generating a plurality of bands of electrical noise, each of said bands having a center frequency on a half-tone of the musical scale, and electrical circuit means for coupling different pluralities of said bands of electrical noise to the electroacoustic output means responsive to each of the electrical switches, each of said pluralities of bands of electrical noise having center frequencies corresponding to a plurality of semi-tones above the frequency of the tone generator connected to said switch of the group consisting of the 12th, 19th, 24th, 28th, 29th, 30th, 32nd, 33rd, 34th, 35th, 37th, 39th, 4lst, 42nd, 44th, 45th, 46th and 47th.

7. The combination according to claim 6, wherein said source of narrow bands of electrical noise comprises a steady white-noise generator, and a plurality of parallel, narrow-band-pass filters coupled to said whitenoise generator.

8. The combination according to claim 4, wherein each of the electrical switches has coupled thereto a second electrical switch, and said second switch is connected between the white noise generator and those band-pass filters associated with the tone controlled by said coupled electrical switch.

9. The combination according to claim 7, wherein the electrical circuit means includes an electronic gate connected between each plurality of narrow band-pass filters and the electroacoustic output means, each said gate being coupled to and controlled by the electrical switch to which said bands of noise are responsive.

10. The combination according to claim 6, wherein said source of narrow bands of noise comprises at least a first continuous white-noise generator, a second continuous white-noise generator, a first low-pass filter coupled to said first noise generator and having a normal and an inverted output, a first plurality of pairs of series-connected photocells, each pair of photocells in said first plurality being coupled across the normal and inverted output of said first filter, a second plurality of pairs of series-connected photocells, each pair of photocells in said second plurality being coupled across the normal and inverted output of said second filter, the total number of pairs of photocells in the first and second plurality being equaled to the number of bands of electrical noise, means for sinusoidally light modulating each pair of photocells at the frequency of a different semi-tone, the photocells of each pair being light modulated out of phase with each other, said electrical circuit means for coupling pluralities of bands of noise being connected to the junction between photocells in selected pairs of photocells.

11. An electrical musical instrument according to claim 6 wherein the source of electrical noise produces bands of noise having center frequencies from about 262Hz through about 8,372Hz.

12. A musical instrument according to claim 11 wherein the narrow bands of noise have Q-values (center frequency/3 decibel bandwidth) of about 13 to about 24, the Q-values increasing with frequency.

Z353? UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,867,852 D d Feb. 25, 1975 I v r) Edward M. Jones and William C. Wayne, Jr.

I: is certified that error eppears in the above-identified patent and that said Letters .Yatent are hereby corrected as shown below:

' Col. 7, Line 58, delete "CC end insert Q Col. 11, Line 6, after "reduced" delete "'by'-' and insert I I Q. Col. l l, Line 53, atter ."approximately" delete "by".

Signed and sealed this 13th day of May 1975.

Attest: Y C. MARSHALL DANN- RUTH C. MASON Commissioner of Patents Attesting Officer I I and Trademarks 533g UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,867,862 Dated Feb. 25, 1975 I m Edward M. Jones and William C. Wayne, Jr.

It is certified that error appears in the above-identified patent and that said Letters .Patent are hereby corrected as shown below:

Q01. 7, Line 58/ delete "CC end insert ,C2# Col. 11, Line 6, after "reduced" delete "by' and insert -l v t I Col; l l, Line 53, after ."approximately" delete "by".

Signed and sealed this 13th day of May 1975.

(SEAL) Y r n I Attest: V i C. MARSHALL DANN' RUTH C. MASON Commissioner of Patents Attesting Officer and Tradeniarks 

1. An electrical musical instrument having a plurality of musical tones corresponding in frequency to the semi-tones of the equally tempered musical scale including an electrical tone signal source for each of the musical half-tones of said instrument, electro-acoustic output means electrically coupled to said sources of tone signals, a plurality of electrical switches, a different one of said switches being electrically coupled to each electrical tone signal source for selectively controlling excitation of the electroacoustic output means, and a source of electrical noise characterized by the improved construction wherein the source of electrical noise has means for generating a plurality of bands of electrical noise, said bands having center frequencies differing approximately by by half-tone steps from each other, and electrical circuit means responsive to each of the electrical switches for coupling a plurality of bands of electrical noise to the electro-acoustic output means, each of said plurality of bands having bands with center frequencies approximately equal to harmonics of that electrical tone signal source coupled to the same electrical switch.
 2. An electrical musical instrument having a plurality of musical tones corresponding in frequency to the semi-tones of the equally tempered musical scale including an electrical tone signal source for each of the musical half-tones of said instrument, electro-acoustic output means electrically coupled to said sources of tone signals, a plurality of electrical switches, a different one of said switches being electrically coupled to each electrical tone signal source for selectively controlling excitation of the electro-acoustic output means, and a source of electrical noise characterized by the improved construction wherein the source of electrical noise has means for generating a plurality of bands of electrical noise, said bands having center frequencies differing approximately by half-tone steps from each other, and electrical circuit means responsive to each of the electrical switches for coupling a plurality of bands of electrical noise to the electro-acoustic output means, each of said plurality of bands having a band with a center frequency approximately equal to a harmonic of a group one through five of that tone signal source coupled to the same electrical switch and a band having a center frequency between adjacent harmonics greater than the fourth harmonic of said tone signal source.
 3. In an electronic organ of the type having in tandem a tone signal generator, a key switch, a tone-color filter, a stop switch and an electroacoustic output system, the combination comprising a source of narrow bands of electrical noise, said bands having center frequencies respectively corresponding to at least a plurality of the semi-tones above the tone signal derived from said tone signal generator by closure of said key switch of the group consisting of the 12th, 19th, 24th, 28th, 29th, 30th, 32nd, 33rd, 34th, 35th, 37th, 39th, 41st, 42nd, 44th, 45th, 46th and 47th partial, and circuit means coupling said source to a point between said key switch and said stop switch for combining said bands with said tone signal.
 4. The combination according to claim 3, wherein said source of narrow bands comprises a wide-spectrum electrical noise generator, a plurality of narrow-band-pass filters coupled in parallel to said noise generator, second circuit means coupled to said narrow-band-pass filters for mixing said bands, and an electronic gate between said second circuit means and said point between said key switch and said stop switch.
 5. The combination according to claim 4, wherein a plurality of leveling resistors are located between respective ones of said narrow-band-pass filters and said second circuit means, and wherein a noise amplifier and a further leveling resistor lie in series between said gate and said point between said key switch and said stop switch.
 6. An electrical musical instrument having a plurality of musical tones corresponding in frequency to the semi-tones of the equally tempered musical scale including an electrical tone signal source for each of the musical half-tones of said instrument, electro-acoustic output means electrically coupled to said sources of tone signals, a plurality of electrical switches, a different one of said switches being electrically coupled to each electrical tone signal source for selectively controlling excitation of the electroacoustic output means, and a source of electrical noise characterized by the improved construction wherein the source of electrical noise has means for generating a plurality of bands of electrical noise, each of said bands having a center frequency on a half-tone of the musical scale, and electrical circuit means for coupling different pluralities of said bands of electrical noise to the electro-acoustic output means responsive to each of the electrical switches, each of said pluralities of bands of electrical noise having center frequencies corresponding to a plurality of semi-tones above the frequency of the tone generator connected to said switch of the group consisting of the 12th, 19th, 24th, 28th, 29th, 30th, 32nd, 33rd, 34th, 35th, 37th, 39th, 41st, 42nd, 44th, 45th, 46th and 47th.
 7. The combination according to claim 6, wherein said source of narrow bands of electrical noise comprises a steady white-noise generator, and a plurality of parallel, narrow-band-pass filters coupled to said white-noise generator.
 8. The combination according to claim 4, wherein each of the electrical switches has coupled thereto a second electrical switch, and said second switch is connected between the white noise generator and those band-pass filters associated with the tone controlled by said coupled electrical switch.
 9. The combination according to claim 7, wherein the electrical circuit means includes an electronic gate connected between each plurality of narrow band-pass filters and the electroacoustic output means, each said gate being coupled to and controlled by the electrical switch to which said bands of noise are responsive.
 10. The combination according to claim 6, wherein said source of narrow bands of noise comprises at least a first continuous white-noise generator, a second continuous white-noise generator, a first low-pass filter coupled to said first noise generator and having a normal and an inverted output, a first plurality of pairs of series-connected photocells, each pair of photocells in said first plurality being coupled across the normal and inverted output of said first filter, a second plurality of pairs of series-connected photocells, each pair of photocells in said second plurality being coupled across the normal and inverted output of said second filter, the total number of pairs of photocells in the first and second plurality being equaled to the number of bands of electrical noise, means for sinusoidally light modulating each pair of photocells at the frequency of a different semi-tone, the photocells of each pair being light modulated out of phase with each other, said electrical circuit means for coupling pluralities of bands of noise being connected to the junction between photocells in selected pairs of photocells.
 11. An electrical musical instrument according to claim 6 wherein the source of electrical noise produces bands of noise having center frequencies from about 262Hz through about 8,372Hz.
 12. A musical instrument according to claim 11 wherein the narrow bands of noise have Q-values (center frequency/3 decibel bandwidth) of about 13 to about 24, the Q-values increasing with frequency. 